1. Field of the Invention
This invention relates to a magneto-optical recording apparatus and may be advantageously applied to a magneto-optical recording apparatus in which record data, for example, may be recorded by overwriting on a magneto-optical disk.
2. Description of the Prior Art
Heretofore, in a magneto-optical recording apparatus, desired record data have been magnetically recorded by taking advantage of the phenomenon that magnetic properties of the magneto-optical disk are changed significantly on both sides of the Curie temperature Tc, which is used as the boundary temperature.
Thus, as shown in FIG. 1, the coercive force Hc of the vertical magnetization film of a magneto-optical disk is lowered abruptly at the Curie temperature.
Hence, the vertical magnetization film is warmed once to higher than the Curie temperature Tc and then lowered to a temperature lower than the Curie temperature Tc by application of an external magnetic field so as to be oriented in the direction of the external magnetic field.
Based on this principle of magnetization, a magneto-optical recording apparatus is so designed and constructed that a light spot sweeps the magneto-optical disk by continuously irradiating the magnetic-optical disk with a light beam to warm up a predetermined region of the magneto-optical disk to higher than the Curie temperature Tc, at the same time that a modulating magnetic field having its polarity reversed at the timing of a predetermined reference clock signal as a function of data to be recorded, is applied with the use of a magnetic head.
In this manner, the region irradiated by the light spot is warmed once to a temperature higher than the Curie temperature Tc and cooled spontaneously so as to be oriented along the direction of the modulating magnetic field applied to the region when crossing of the Curie temperature Tc occurs.
Thus, even when a pattern of magnetization has been formed previously, micro-regions oriented in accordance with the modulating magnetic field (referred to hereinafter as magnetized domains) are formed sequentially along the sweeping path of the light spot at the period of the clock signals to cause desired record data to be recorded in an overwriting manner.
However, when the region irradiated by a light beam is cooled spontaneously after the irradiation, the time which elapses from sweeping by the light spot until spontaneous cooling to lower than the Curie temperature Tc changes as a function of the temperature characteristics of the magneto-optical disk itself, so that a problem arises in that the magnetized domain formation position changes with respect to the reference clock signal as a function of temperature characteristics of the magneto-optical disk itself.
Hence, when forming reference clock signals from servo patterns previously formed on the magneto-optical disk, the magnetized domain forming position with respect to the servo patterns changes so as to render it difficult to reproduce record data on the basis of the servo patterns. Thus, phase shift or deviation occurs in the signal reproduced from the servo patterns.
In addition, for reliably detecting changes in orientation between adjoining magnetized domains and reliably reproducing the record data, it is necessary to form magnetization patterns having an orientation which is reversed abruptly between the adjoining magnetized domains.
Thus, when the light beam is irradiated continuously, it becomes necessary to provide a circuit for forming the modulating magnetic field which includes a driving circuit having excellent frequency characteristics, so as to enable abrupt polarity inversion of the modulating magnetic field, which complicates the structure on the whole correspondingly.